A comprehensive study on the performance of Submerged Floating Tunnels during severe seismic events

The Submerged Floating Tunnel is an innovative solution for waterway crossings, consisting in a tubular structure floating underwater and fixed in position by means of tensioned anchorages linked to the seabed. SFTs seem to be particularly suitable to cross waterways located in high seismicity zones, due to their large transversal flexibility and to the additional damping and inertia arising from the water-structure interaction. The seismic behaviour of SFTs features peculiar aspects that deserve to be studied, such as the influence of the asynchronous ground motion and of the propagation of vertical ground motion in the upper water layer. In order to investigate the structural response and performance of SFTs during an exceptionally severe earthquake, the 1908 Messina (Italy) earthquake is simulated, generating acceleration and velocity time histories in the ground and in the water layer. An extensive campaign of F. E. analyses is carried out, considering several structural configurations, differing for the set up of the anchoring system and the values of the crossing length. A brief overview of the main results of the study is given in this paper.